1. Field of the Invention
The present invention relates to a fuel tank made from a thermoplastic synthetic resin and more particularly to an automotive fuel tank whose outer wall is formed from a thermoplastic synthetic resin through blow molding and which has a built-in part in an interior thereof.
2. Related Art
Conventionally, metallic fuel tanks were used as fuel tanks for motor vehicles and the like. In recent years, however, fuel tanks made from thermoplastic synthetic resins have been in use due to thermoplastic resin materials being light in weight to satisfy increasing demands for vehicles which are light in weight, being free from rust, being easy to be molded into desired shapes.
A blow molding approach has been used in many cases in fabricating automotive fuel tanks from thermoplastic resins because the blow molding approach facilitates the molding of hollow objects. In the blow molding approach, a parison made of a molten thermoplastic synthetic resin member is extruded into a cylindrical shape from above, and air is blown into the parison while the parison is being held by molds to thereby fabricate an automotive fuel tank.
On the other hand, also in the blow molding approach, it is required to provide built-in parts such as valves and baffle plates for suppressing flowing or lapping noise of fuel in an interior of a fuel tank.
Then, to make this happen, there has been proposed an approach in which a built-in part 120 is set in a resin frame, and the resin frame is set within a mold, so that the built-in part 120 is made to be secured to an inner circumferential surface of an outer wall of a fuel tank through blow molding, whereby the built-in part 120 is mounted in an interior of the fuel tank (for example, refer to JP-A-1-301227).
In this case, however, since the built-in part 120 is set in the resin frame and is then secured to the inner circumferential surface of the outer wall of the fuel tank, labor hours have to be involved in cutting to remove the resin frame after the fuel tank has been molded, and with a small built-in part 120, a large resin frame has to be used, often resulting in a case where the weight of the molded fuel tank is increased.
In addition, there has been proposed a fuel tank in which a built-in part is provided in an interior thereof in a way as illustrated in FIGS. 15 to 16 (for example, refer to JP-A-6-143396).
In the fuel tank, firstly, as is shown in FIG. 15, a built-in part 220 is placed on a holding rod 241 before a parison 208 is set in a blow mold 240. Thereafter, with the blow mold 24 left opened, the parison 208 is lowered, so as to position the built-in part 220 in an interior of the parison 208.
Thereafter, as shown in FIG. 16, press pins 242 are made to project inwards from both sides of the blow mold 240 before the blow mold 240 is closed to press against the parison 208, so as to press the parison 208 to side ends of the built-in part 220. As this occurs, since an inner surface of the parison 208 has not yet been set then, the parison 208 and the side ends of the built-in part 220 can be fusion bonded together.
Then, the holding rod 241 is lowered, the blow mold 240 is closed, and air is blown into the parison 208 for blow molding.
In this case, an abutment surface 233 formed at a distal end of the built-in part 220 for abutment with the parison 208 and the inner surface of the parison 208 are only brought into simple contact with each other, and the abutment surface 233 does not penetrate into an interior of the parison 208. Thus, there occurs only weak adhesion therebetween, and fusion bonding strength is not sufficiently large, leading to a fear that the abutment surface 233 may be separated from the inner surface of the parison 208 due to vibration of fuel in the fuel tank or expansion of the fuel tank.
In addition, there has been proposed a fuel tank in which upper and lower outer wall portions are recessed to contact each other for fusion bonding over several locations on the fuel tank in order to increase the strength thereof. In this case, however, since the outer wall portions are partially recessed to contact each other for fusion bonding, an interior volume of the fuel tank is reduced.